Hi CK8,
Sorry to drag up an old query, but am after some more information on what you did here?
I am in the same boat with a client, and hate hate hate the lack of security available in the DEVG2020.
I can't even get a site-to-site VPN configured due to the poor implementation in this device.
From what i understand of your resolution, you have the following setup
NBN goes to WAN DEVG2020
Cisco connects to 1 port of DEVG2020
Draytek connects to 1 port of DEVG2020
You are then either using specific port forward blocks or DMZ to transfer all traffic to the Draytek?